Deep water platform construction

ABSTRACT

A self-erecting offshore platform for deep water installations comprised of three or more (optimum four) leg modules, and one platform module, all of which are buoyant and towable to an offshore site. At a site location the leg modules are pivotally interconnected to the platform and rigged with cables for limiting their relative lateral motion while being pivoted into contact with the ocean floor. The pivoting action is obtained by decreasing the buoyancy of the outer (lower) ends of the leg modules. Upon initial positioning of the leg modules in contact with the ocean floor, they are then lightened by expelling water from their upper buoyancy chambers. The lower ends of the leg modules are drawn toward one another as increased buoyancy in their upper ends raises the platform out of the water. When predetermined elevation of platform has been reached, the supporting foot pads (mats) are pivotally moved downward to flat contact with the ocean bottom by flooding their upper buoyancy tanks.

United States Patent 11 1 McDonald et al.

[ Dec. 2, 1975 DEEP WATER PLATFORM CONSTRUCTION [75] Inventors: ReaganW. McDonald; Walter B.

Joseph, both of Houston, Tex.

[73] Assignee: Reagan W. McDonald, Houston,

Tex.

[22] Filed: Aug. 27, 1974 [21] Appl. No.: 500,913

[52] U.S. Cl 6l/46.5; 114/.5 [51] Int. Cl. E02D 21/00 [58] Field ofSearch 61/465, 47, 50, 46; 114/05, 26, 31, 50; 175/7, 8, 9; 166/.5, .6

[56] References Cited UNITED STATES PATENTS 2,600,76l 6/1952 Halliburton6l/46.5

Primary Examiner-Dennis L. Taylor [57] ABSTRACT A self-erecting offshoreplatform for deep water installations comprised of three or more(optimum four) leg modules, and one platform module, all of which arebuoyant and towable to an offshore site. At a site location the legmodules are pivotally interconnected to the platform and rigged withcables for limiting their relative lateral motion while being pivotedinto contact with the ocean floor. The pivoting action is obtained bydecreasing the buoyancy of the outer (lower) ends of the leg modules.Upon initial positioning of the leg modules in contact. with the oceanfloor, they are then lightened by expelling water from their upperbuoyancy chambers. The lower ends of the leg modules are drawn towardone another as increased buoyancy in their upper ends raises theplatform out of the water. When pre-determined elevation of plat-2,772,539 12/1956 Sandberg.... 61/465 form has been reached, theSupporting foot pads g (mats) are pivotally moved downward to flatcontact 3 327 668 6/1967 Vil s c bin; 'g' 5 with the ocean bottom byflooding their upper buoy- 3.673973 7/1972 Glosten 114/.5 D ancy tanks-3,739,737 6/1973 Baler 114/.5 D 13 Claims, 7 Drawing Figures 1 1 t Q *471w? Z -Kv US. Patent Dec. 2, 1975 Sheet 1 of 3 3,922,868

US. Patent Dec. 2, 1975 Sheet 2 of3 3,922,868

U.S. Patent Dec. 2, 1975 Sheet 3 of3 3,922,868

oo o o ofio I lad 1f DEEP WATER PLATFORM CONSTRUCTION FIELD OF THEINVENTION This invention relates to offshore platforms and moreparticularly to systems for erecting offshore platforms in water depthsin excess of 450 feet.

BACKGROUND OF THE INVENTION Offshore platform construction in deep wateris a complex problem of technology. Time and equipment involved becomevery critical due to the great expense incurred in offshore operations.In deep water, divers have limited capabilities and submersible divingequipment is expensive and slow going in actual use. In U.S. Pat. No.2,857,744 a system is proposed where an entire structure is towed to alocation and tilted from a horizontal to a vertical position. Thissystem has limitations as to the effective depth that can be reached bythis system and the complexity of handling an extremely large piece ofequipment. Design factors also limit the depth at which a structure ofthis type can be used. In U.S. Pat. No. 3,253,417, a system is proposedwherein the entire platform is hinge connected together and the base issubmerged first. This system lacks control of the components andrequires a certain amount of precision which is difficult to obtain inlarge structures.

The foregoing systems lack structure configurations which are stableboth in the transportation to the site and upon erection at the site. Inthe present invention, a modular multiple articulated system providesfor easy transportation, and a stable structural configuration duringall phases of construction and operation.

SUMMARY OF THE INVENTION The present invention is embodied in a systemwherein an optimum of four leg modules and a platform module for anoffshore platform are made selectively buoyant, and are independentlytowable to an offshore location site. At the location site, the legmodules and platform module are pivotally interconnected. Support matsor pad members, while still in protected waters, are attached to theirrespective leg modules by massive pins which are capable of transmittinglarge values of thrust and transverse moment. Each leg module isconstructed from three equidistantly spaced tubular members which arelaced together by tubular webs or spacing members. An alternative designincluded in this concept would be to use a single large tube for eachleg module rather than three smaller tubes laced together. Each supportmat may be rectangularly shaped in plan view. Cables are provided toextend along the length of each leg module, from winches mounted at thetop, and are anchored at remote locations on the ocean floor in order tofurnish lateral control while lowering the leg modules.

At the site location, the platform module is anchored by four largeanchor cables or chains extending diagonally away from the corners ofthe platform. Each cable can be connected to its own winch for control.The leg modules, which are pivotally connected to the platform module,contain buoyancy compartments which are selectively flooded toaccomplish smooth, slow submergence. After all of the support matsengage the ocean floor, the buoyancy of the leg modules is selectivelyincreased beginning at the top, to bring the leg modules toward oneanother and to lift the platform above the 2 water level. At theprecalculated elevation and altitude of the legs, the support mats areflooded to rotate them into final position flat on the ocean floor. Allfour mats are interlocked by tie cables or chains, and the structure isin its final position. No diiving operations are necessary for thiserection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a leg member andsupport mat in towing position;

FIG. 2 is a view taken along line 22 of FIG. 1;

FIG. 3 is a plan view of the structure as it is assembled prior tosubmergence of the leg modules;

FIG. 4 is a side view showing a leg module in an ocean floor touchingposition;

FIG. 5 is a side view showing a leg member in a position just prior tothe rotating of a support mat member;

FIG. 6 is a side view illustrating the assembly in an erected position;and

FIG. 7 is a view taken along line 77 of FIG. 6.

BACKGROUND OF THE INVENTION Referring first to FIG. 3, an offshoreplatform 10 is schematically illustrated in a plan view where themembers are floating in the water prior to submergence of the legmodules. In FIG. 6, a side view illustrates the platform 10 as locatedin position on an offshore site.

In FIG. 3, the platform body module 11 is illustrated with a generallysquare shaped configuration defined by sides 11a, 11b, 11c, and 11d,although it will be appreciated that the configuration can assume othershapes. At pivot points 12a, 12b, 12c and 12d midway of the length ofeach side, a load supporting leg module 13a, 13b, 13c and 13d ispivotally connected to the platform body 11 by a massive pin. Asillustrated in FIG. 6, in the final assembly position, the leg modules13 a-d are disposed at an acute angle with respect to a vertical.Pivotally connected to the lowermost ends of the leg modules l3( a-d)are support mats 14 a-d which are illustrated with a generallyrectanguar configuration. Depending spuds 15 a-d from the mats 14 a-dare embeddable into the underwater ocean floor l6 and prevent shiftingof the support mats relative to the ocean floor. The leg modules 13 a-dhave a length adequate to suspend or support the platform body 11 abovethe surface 17 of the water. Each of the support mats l4 a-d isconnected to both adjacent support mats by a chain or cable 18 a-d (seeFIG. 7).

The completely assembled platform assembly is basically comprised of theplatform module 1 1 and the four supporting leg modules 13 a-d. Each ofthe leg modules is constructed to have buoyancy chambers, such as thechambers lle, 13c and 15e illustrated in FIG. 2. The buoyancy of the legmodules permit the leg modules to be towed in a floating orsemi-submerged condition to the selected offshore location. At theselected location, the individual leg modules 13 a-d are pivotallyinterconnected at pivot connections 12 a-d, while floating, to the sides11 aa' of the platform body module 1 1. The legs 13 a-d and mats 14 a-dare then selectively (or simultaneously) controlflooded in such mannerthat their outer ends submerge and slowly sink to engage the oceanfloor, while upper ends, which are pinned to platform module 1 1, remainbuoyant. The support mats are pivotally connected to the support legmodules at 20 a-d. When water is expelled from upper ends of the legs,their increasing buoyancy lifts them and the platform'module 11 suchthat it rises out of the water to a predetermined elevation. Then thesupport mats 14 u-d are pivoted into anchoring position on the oceanfloor 16 by flooding their chambers.

Referring now in FIG. 1, one typical load-supporting leg module 13a isillustrated in a floating position in the water. The leg module will beseveral hundred feet in length, as necessary for the desired height ofthe platform above the water level. Each leg module is separatelyfabricated and separately launched so that it can be independently towedto the platform site location in the body of water. If desired, a pad lecan be outfitted with marine propulsion equipment (not shown). Asillustrated in FIGS. 1 and 2, the support leg module 1330 consists ofthree generally cylindrically shaped and elongated tubular elements 22ac which are equidistantly spaced from one another by transverse trussweb members 23 ac. These web members 23 ac may also be tubular. Thetruss web members 23 ac are angularly disposed with respect to thelengthwise axis of Iongitudinal members 22 ac and suitablyinterconnected thereto. At the upper end of the supporting leg module13a is a connecting frame means 24 which is adapted for pivotalconnection at a location 12a to the platform body module. As illustratedin FIGS. 1 and 2, the connecting frame means 24 included an upper platemember 25 which is attached to and made a part of two supporting tubularelements 22a and 22b so as to intersect and lie in a plane coextensivewith the longitudinal axis of the two supporting elements 22a and 22b.The plate member 25 has a pivotal means 12a with a pivot axis disposedin a plane transverse to the lengthwise axes of the supporting members22a and 2219. A depending support means 26 extends from the transversepivotal means 12ato the remaining supporting element 22c. At the otherend of the supporting element 13a is a pivot means 20a for providing apivotal connection to the mat member a. The mat member 15a may berectangular in section and has a hollow interior which is divided intoforward and rearward compartments 27 and 28. The forward compartmentbeing to one side of the axis of the pivot connection and the rearwardcompartment being to the other side of the pivot connection. In thepivot position illustrated, the upper face 30 of a mat member and thelower surface 31 are generally parallel to the plane through thesupporting elements 22a and 22b. On the upper face of the supporting matare transverse anchor spuds 15a which can be embedded in the subseaformation strata. The spuds 15a, as shown in FIG. 1, are retracted inthat they face outwardly from the upper face 30 for towing purposes.At.a site location, the spuds are extended through the lower surface 31and locked into position by suitable means (not shown).

Along the length of each of the supporting elements 22 ac and forapproximately the mid-third portion thereof, the main tubular supportingelement 22 a-c may be surrounded or encased by an outer concentri-Cally-arranged tubular member 32 a-c to form an annular floatationchamber 33 0-6. While reference is made here to a single chamber, itwill be appreciated here and elsewhere that multiple chambercompartments and common control valves can be used. By appropriateflooding of the chamber 330 in the leg element and one of the chambers27 in the foot mat member, a leg element 13a can, if desired, bepartially submerged for towability and yet be sufficiently buoyant topermit an easy tow. As illustrated in FIG. 1, the leg member is inclinedwith pivot end 12a submerged and the mat member 15 at an incline. Thus,the member can be moved to the right with any suitable towing or motormeans.

All leg modules 13a-d and the platform module 11 are independently towedto the selected platform site. The platform module 11 may be madebuoyant by construction or by float means as desired. At the selectedsite, the leg modules 13 ad are aligned with the platform body 11 sothat the pivotal interconnections 12 a d between the leg modules 1 1a-a' and platform 11 can be made. The platform module 11 is anchored inplace by corner cables 38 awhich extend from corresponding winches onthe platform at 45 angles to the platform sides to retrievableunderwater anchors (not shown). The cables 38 a-d, by control of thewinches, maintain the position of the platform module 11. On each legmodule a dual cable system 39 ad and 40 ad extends from separate winches41 and 42 on the platform 11 along guides (not shown) disposed along thelength of the leg module to pulleys at the end of the leg element. Fromthe end of each leg module, the cables 39 a-d are extended transverselyto a leg module and lie in a vertical plane. The ends of the respectivecables are anchored to the ocean floor at suitable distances from theends of the leg members by suitable retrievable anchors. Upon actuationof the winches 41 and 42 and control of the forces on the cables, theouter ends of all leg members can be maintained in proper alignment andorientation with respect to the platform body 11 while they are floodedand slowly lowered to the bottom. The cables also provide a control sothat excess force is not applied to the pivot connections 12 a-d. Whenthe pins are in place, the entire system gives the appearance ofgigantic pinwheel lying flat on the surface of the water.

While not shown, the chambers 33 ac can be compartmentalized along thelength of the leg modules so as to selectively flood the compartments ofa leg module beginning at the end of the leg module nearest the matmember 15a. This will insure an even disposition of the forces and canbe controlled by any suitable control system. Any water in chamber 27 ofthe anchor mat 15a is pumped into the chamber 28 to provide a clockwiseforce about the pivot 20a and to maintain the pad in the alignedposition. The lowering of the end of a leg module continues until theends 42 of the mat members engage the floor 16 of the ocean asillustrated in FIG. 4. Because of the flooding of the lower tank chamber28 of the mat members, the mat members are kept in an aligned positionwith respect to the leg modules. During this phase, the platform module1 1 continues floating and buoyant.

In the position shown in FIG. 4, the water ballast contained in upperchambers 33 ac in the leg modules is expelled to provide buoyant liftingforces, the center of which is designed to remain always above thecenter of gravity to prevent any possibility of capsizing. As watercontinues to be expelled from the upper chambers of the leg modules, theentire interconnected system of platform body 11 and legs 13 ad continueto rise, causing the lower ends of the leg modules 13 ad with theirpivoted mats 14 ad to move toward each other along bottom of the ocean.As the platform module rises, the

lower ends of the mats will be dragged by gravity toward each otheralong the bottom of the ocean.

As an alternative, a winch 44 and cable 45 (shown in FIG. 5) can be usedto assist in drawing the leg modules toward one another. A cable 45 canbe passed over a pulley 46 to extend horizontally to an opposite legmodule. As shown in FIG. 5, the cable 45 would extend to the leg member13c while a cable 48 from leg member 130 extends to leg member 13a andis attached thereto by a sling connector 49. By simultaneously applyingtension to cables connected to all of the mid-sections of the legmembers, the lifting of the platform 1 1 relative to the level 17 of thewater can be accomplished.

In the position shown in FIG. 5 the compartments 27 in the anchor mat14a are filled with water to decrease the buoyancy. An anchor mat pivotsabout the pivotal connection a into a position where the spuds 15a areembedded into the ocean floor under the mat. Each of the leg members andmat members is provided with a suitable mechanical or hydraulicinterlock 50 which is actuated from the platform 11 above water andrigidly connects the leg member and mat member.

The stabilizer chains 18 ad, when required for a particular type ofbottom soil condition, are transported to the drill site in separatesegments lying in guideways (not shown) prepared along each leg 13 a-d.After rotation of anchor mats 14 a-d into final flat position on theocean floor and before flooding the upper leg buoyancy compartmentswhich lifted the platform out of the water, the upper ends of thesechains 18 a-d between each pair of adjacent legs, such as 13a and 13b,are joined at a location 52 above water (See FIG. 6) with assistance ofthe deck cranes (not shown). Then by means of winches connected to theother ends of the cables and pulleys (not shown) at the lower ends ofleg modules 13 a-d, the chains 18 ad are drawn down and locked intofinal position as shown in FIG. 7.

Summarizing the method of the present invention, it involvesconstruction of a marine platform at an offshore location site in verydeep water, wherein the platform consists of an above-water platformmodule plus at least three supporting leg modules. Each of the legmodules is comprised of a leg, proper, and a pivotally interconnectedfoot pad or mat. The method consists of the following major steps:

1. Separate fabrication of the several modules and sub-modules (even atdifferent fabrication plants, if necessary or desirable),

2. Separate launching of the several modules and sub-modules,

3. Separate towing the each completed molule by one or more tugs acrossthe open ocean to the selected location site for rendezvous with allcompanion modules. A minimum of four modules is necessary for anon-drilling three leg platform, whereas six or more modules arerequired for a drilling platform,

4. Mating and pivotally interconnecting of each leg sub-module 13a toits own mat sub-module 14a while in protected water facilitated bypartial flooding of selective buoyancy compartments 27 at inner end ofthe mat and 336 at the far (upper) end of the leg,

5. Temporary anchorage of the platform module 11 with the anchor cables38 a-d in such manner as to maintain precise location during theerection sequence without interfering with said sequence,

6. Careful maneuvering by tugs of each leg module 13 a-d into correctposition with respect to the platform module 11, then temporary lateralanchoring of the outer mat ends of all leg modules with the cables 39a-d and 40 a-d so as to limit and restrain the relative lateralmovements of the leg modules, I

7. Connecting the inner ends of all leg modules 13 a-d by cables towinches mounted on the deck of the platform module, then winchin g allthe legs into their respective guideways prepared in the platformmodule, and securing them all together by inserting and locking the pinsin place. When this step is completed, the entire system will form agigantic pinwheel lying flat on the surface of the ocean, andarticulated with respect to the water plane at all connection pointsbetween modules and sub-modules,

8. Sinking the outertips of the leg modules 13 a-d (outer edges of matsub-modules) until they touch the bottom of the ocean, by carefullycontrolled selective flooding of the tanks, with progressively greaterflooding taking place toward outer tips. During this phase, the platformmodule 11 continues floating and is totally buoyant, providing therequired stability to prevent any and all modules from capsizing,

9. The platform module is lifted out of the water (actually lifting theentire platform assembly, including the legs and the mats), by means ofprogressively increasing buoyancy of the upper ends of the legs, throughcarefully controlled selective expulsion of water from the buoyancycompartments. Precalculations for each platform design will insure thatfor each said design, the center of buoyancy will always remain abovethe center of gravity, permitting no tendency to capsize. As theplatform assembly rises, the lower tips of the mat sub-modules will bedragged by gravity toward each other along the bottom of the ocean. Thelifting phase will be terminated at a predetermined elevation of theplatform module 11 above the water, with the bottom (outer) edges 42 ofall mat submodules in contact with the ocean floor, and with all forces(buoyancy and gravity still in a stable state of equilibrium, 7

10. The mat sub-modules 14 a-d are pivoted about their bottom (outer)edges 42 which are in contact with the ocean floor, so as to bring thebottoms of the mats down flat on the ocean floor. If the spuds 15 ad arerequired for a given location, they will be forced to penetrate into theocean floor under the mat bottoms. While all the mats are pivoting abouttheir outer edges, another simultaneous pivoting motion will be occuringat all of the mat pin connections between the legs and the mats,changing the angle between the axis of each leg with respect to the axisof its corresponding mat from nearly parallel, to about 65. At the sametime, a third set of simultaneous pivoting motions will be taking placeat all main pins which connect the legs to the platform module. When allof these carefully controlled pivoting actions have been completed,

the entire platform assembly will be seated in final I position on theocean floor,

l l. The mat tie chains 18 a-d which were transpofted the bottom. Whenall chains have been lowered to the bottom and snugged-up with the deckwinches, they are then locked in position so that they will permanentlyprevent horizontal movement of the mats relative to each other,

12. Fill-in and support members 54 are added between the platform andupper ends of legs for strength,

13. Locking mechanisms 50 on the mats are actuated to prevent anyfurther change in the angles between the legs and the mats. Theselocking mechanisms, where deemed necessary for a particular design (theymay not be required at some locations), can be hydraulic and reversible.Their use will ap preciably increase rigidity of the structure, andreduce flutter of the slim legs due to wave action,

14. The legs can then be reflooded in order to firmly seat the mats intothe mud on bottom of the ocean, and provide sufficient gravitationalanchorage to prevent dislocation of the platform by storm forces. Whenthis is completed, then all compartments is all legs and mats willbecome available for underwater storage of oil, utilizing the samepiping and valving which was used for control flooding and dewateringduring the erection sequence, with all valves located above water.

In the present system, the drilling conductors can also be floated to anoffshore location site in very deep water. The conductors are bundledtogether into an integral structural package of sufficient strength tospan or extend vertically from ocean bottom to the platform above. Thefabrication of the conductor bundle is accomplished at a location whereit can be launched like a ship or barge. It consists of several parallelrows of conductors, for example, 30 inch diameter pipes trussed togetherin both directions with smaller pipes at appropriate angles and spacingthroughout their full lengths. The length of the pipes is about 50 feetgreater than the water depth at the drilling location. All of theconductors have water-proof closures at both ends, the lower endsprobably being closed with rubber diaphrams which are commerciallyavailable. The conductor bundle is suitably valved at each end in suchmannner that flooding can be precisely controlled from above water. Atypical conductor bundle can be constructed in a similar manner to a legmodule such as illustrated in the drawings without the pad or mat andwithout the hinge connection.

A conductor bundle is lauched and towed to the drilling location by oneor more tugs. At the location, controlled flooding of one end of theconductor bundle is performed while the opposite end is held inapproximate location by moderately tensioned cables to the platform.This step is completed when the bundle is floating in vertical attitudewith its lower end a few feet above bottom of the ocean. Furtherflooding of the bundle after precise location is accomplished in orderto sink the lower end into the mud and fix it in location so that nomore horizontal movement can occur. At this time, another section can beadded on at top of the bundle. The prefabricated add-on will be shorter,perhaps only 50 or 100 feet, and may be transported on a barge, insteadof floating, but will otherwise be like the main bundle. This add-onwill take considerable time to complete all of the welding. Temporaryclosures at the top of the main bundle will also be removed at thistime. Further flooding of the bundle will force its lower end furtherinto the bottom of the ocean. Since total flooding will not producesufficient penetrationfor safe anchorage and safe support of wells andwellheads, sea water is pumped into the tanks on the top of the bundleto cause more penetration, as required for load support. When finalpenetration is obtained, the upper end of the conductor bundle will belaterally secured to the platform in such manner that differentialvertical settlement can be accommodated without causing structuraldistress. The conductor bundle will then be vertically and horizontallysupported at mud line, and horizontally supported at the platform level,and its own flexural strength will permit it to span as a vertical beambetween top and bottom, resisting wave forces.

The advantages of the present system are that all fabrication, erectionand operational work are accomplished above water, under atmosphericconditions and no diving or submarine work is required. No pile-drivingof the type normally required for template type steel platforms will berequired. No derrick barge or derrick ship will be ordinarily requiredfor initial installation. However, a derrick barge may be needed if someequipment modules later need to be changed out during switchover from apredominantly drilling operation to a predominantly productionoperation. Also, still later, when compression becomes necessary, aderrick barge will again be needed to change out equipment modules. Theseveral anchors and cables (also Winches) used during the erection canbe salvaged almost immediately if desired and reused on other projects.The entire platform assembly including legs and mats can be totallysalvaged and re-erected at a different location if necessary. A largevolume of oil can be temporarily stored under water, within the legs andmats of this platform, during the production phase of its useful life.

While particular embodiments of the present inven tion have been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention is its broader aspects; andtherefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. A method for erecting a marine platform at a deep water offshorelocation site where the platform consists of a surface platform moduleand at least three supporting leg modules, the method comprising thesteps of floating each of platform and supporting leg modulesindependently to an offshore site,

at a given offshore site, pivotally interconnecting the leg modules atone of their ends to the platform module,

increasing the density of said leg modules at their other ends so as topivot said leg modules about the pivotal interconnection until saidother ends of said leg modules are in engagement with the ocean floor,

after said other ends of said leg modules are in engagement with theocean floor, decreasing the density of the upper ends of said legmodules and pivoting said leg modules further about the pivotalinterconnection to raise said platform member above the surface of thewater.

2. The method as defined in claim 1 and further including the step ofanchoring said other ends of said leg modules in the ocean floor aftersaid platform module is raisedabove the surface of the water.

3. The method as defined in claim 1 wherein said leg modules are floatedto the offshore site with their lengthwise dimension in a nearlyhorizontal position.

4. The method as defined in claim 3 wherein the density of the legmodules is increased by filling hollow interiors of the leg modules withwater, and further including the step of maintaining counterbalancingforces on each leg module while it is being pivoted into position.

5. A method of erecting a marine platform at an offshore location sitewhere the platform consists of a surface platform module and three ormore supporting leg modules, and where each of said modules havebuoyancy chambers along their length, and each of said leg modules havepivotally connected anchor mats at an outer end thereof, the methodcomprising pivotally connecting each of said supporting leg modules inhorizontal positions, respectively, to one of the sides of said surfaceplatform module,

filling said buoyancy chambers of said leg modules with water beginningat the outermost ends of said leg modules for tilting said leg modulestoward near vertical positions until the outermost ends of said anchormats engage the bottom of the ocean floor,

increasing the buoyancy of said leg modules while moving said legmodules to a desired near vertical attitude for raising said platformmodule above the level of the water, and

pivoting said anchor mats to an anchoring position with respect to theocean floor.

6. The method as defined in claim 5 and further including the step ofmaintaining an anchoring surface of said anchor mats in alignment withthe lengthwise dimension of a leg module until said platform module iselevated above the surface of the water, and thereafter pivoting saidanchor mats relative to a leg module by placing the anchoring surfaceinto engagement with the ocean floor.

7. The method as defined in claim 6 wherein said pivoting of said anchormats is followed by the step of locking said leg module and an anchormat in position relative to one another.

8. The method as defined in claim 6 and further including the step ofmaintaining counterbalancing lateral forces in a direction transverse toa leg module while it is being pivoted into an anchoring position.

9. A method for erecting an offshore platform in deep water comprisingthe steps of floating separate modules of said platform to an offshoresite where said modules include a surface platform and legs, said legmodules including buoyancy chambers for controlled flooding andexpelling of water,

at the offshore site, anchoring said platform at a site position,connecting all of the legs pivotally to said platform while said legsare in a nearly horizontal position, extending transverse cables inopposite directions from the outermost ends of said legs and connectingsaid cables through the length of said legs to winches on the platform,

flooding the outermost ends of said legs with water and controlling thelateral forces on the legs with said transverse cables to pivot saidlegs into a nearly vertical position, until the outermost ends of saidlegs engage the bottom of the ocean floor, and expelling water from saidlegs to increase their buoyancy for lifting said platform out of saidwater while pivoting said legs to an anchoring position and 10maintaining the center of buoyancy above the center of gravity for theassembly. 10. The method as defined in claim 9 and further including thestep of floating a conductor bundle to the site location in a horizontalcondition where said bundle has buoyancy chambers for control floodingof water,

at the site location, after the platform is raised, flooding theoutermost end of said conductor bundle while fixing the location of theother end relative to the platform until the conductor bundle is in avertical position,

maintaining said bundle in a vertical position off of the ocean floorand moving said bundle into location relative to said platform module,and

filling said bundle with water to set it in location for welloperations. 11. A method for erecting an offshore platform in deep watercomprising the steps of floating separate modules of said platform to anoffshore site where said modules include a surface platform and legmodules, said leg modules including buoyancy chambers for controlledflooding and expelling of water, said leg modules further including matmodules pivotally interconnected to the outermost ends of said legmodules, said mat modules having buoyancy chambers for controlledflooding, flooding said mat modules so as to maintain said mat modulesin general horizontal alignment with the length of said leg modules, atthe offshore site, anchoring said platform at a site position,connecting all of the leg modules pivotally to said platform while saidleg modules are in a nearly horizontal position, extending transversecables in opposite directions from the outermost ends of said legmodules and connecting said cables through the length of said legmodules to winches on the platform, flooding the outermost ends of saidleg modules with water and controlling the lateral forces on the legmodules with said transverse cables to pivot said leg modules into anearly vertical position and maintaining said mat modules in generalhorizontal alignment with the leg modules while said leg modules arepivoted so that said mat modules are brought into engagement with theocean floor, and

following the expelling of water from said leg modules, the step offlooding said mat modules with water to pivot said mat modules intoanchoring position with the ocean floor.

12. The method as defined in claim 11 and further including the step ofinterconnecting one end of chains extending from each of said legs atthe platform where the chains extend along the length of a leg and passover a pulley at the outermost end of a leg and return to the other endof the leg, and

after interconnecting the one end of said chains, taking up the slack inthe other ends of said chains to position said chains as aninterconnection between the outermost ends of said legs.

13. A marine platform for deep water installation comprising a surfaceplatform module,

at least four supporting leg modules disposed at locations lying onperpendicular, intersecting, horizontal axes, means pivotally connectingone end of said leg modules to said surface platform module, said pivotmeans respectively having pivot axis at said locations in a positionnormal to an axis, each 11 12 of said leg modules including tubularmembers arpartments, and ranged in an equidistant triangularrelationship means for selectively flooding said buoyancy comwithinterconnecting support members, each of partments with sea water. saidtubular members including buoyancy com 5

1. A method for erecting a marine platform at a deep water offshorelocation site where the platform consists of a surface platform moduleand at least three supporting leg modules, the method comprising thesteps of floating each of platform and supporting leg modulesindependently to an offshore site, at a given offshore site, pivotallyinterconnecting the leg modules at one of their ends to the platformmodule, increasing the density of said leg modules at their other endsso as to pivot said leg modules about the pivotal interconnection untilsaid other ends of said leg modules are in engagement with the oceanfloor, after said other ends of said leg modules are in engagement withthe ocean floor, decreasing the density of the upper ends of said legmodules and pivoting said leg modules further about the pivotalinterconnection to raise said platform member above the surface of thewater.
 2. The method as defined in claim 1 and further including thestep of anchoring said other ends of said leg modules in the ocean floorafter said platform module is raised above the surface of the water. 3.The method as defined in claim 1 wherein said leg modules are floated tothe offshore site with their lengthwise dimension in a nearly horizontalposition.
 4. The method as defined in claim 3 wherein the density of theleg modules is increased by filling hollow interiors of the leg moduleswith water, and further including the step of maintainingcounterbalancing forces on each leg module while it is being pivotedinto position.
 5. A method of erecting a marine platform at an offshorelocation site where the platform consists of a surface platform moduleand three or more supporting leg modules, and where each of said moduleshave buoyancy chambers along their length, and each of said leg moduleshave pivotally connected anchor mats at an outer end thereof, the methodcomprising pivotally connecting each of said supporting leg modules inhorizontal positions, respectively, to one of the sides of said surfaceplatform module, filling said buoyancy chambers of said leg modules withwater beginning at the outermost ends of said leg modules for tiltingsaid leg modules toward near vertical positions until the outermost endsof said anchor mats engage the bottom of the ocean floor, increasing thebuoyancy of said leg modules while moving said leg modules to a desirednear vertical attitude for raising said platform module above the levelof the water, and pivoting said anchor mats to an anchoring positionwith respect to the ocean floor.
 6. The method as defined in claim 5 andfurther including the step of maintaining an anchoring surface of saidanchor mats in alignment with the lengthwise dimension of a leg moduleuntil said platform module is elevated above the surface of the water,and thereafter pivoting said anchor mats relative to a leg module byplacing the anchoring surface into engagement with the ocean floor. 7.The method as defined in claim 6 wherein said pivoting of said ancHormats is followed by the step of locking said leg module and an anchormat in position relative to one another.
 8. The method as defined inclaim 6 and further including the step of maintaining counterbalancinglateral forces in a direction transverse to a leg module while it isbeing pivoted into an anchoring position.
 9. A method for erecting anoffshore platform in deep water comprising the steps of floatingseparate modules of said platform to an offshore site where said modulesinclude a surface platform and legs, said leg modules including buoyancychambers for controlled flooding and expelling of water, at the offshoresite, anchoring said platform at a site position, connecting all of thelegs pivotally to said platform while said legs are in a nearlyhorizontal position, extending transverse cables in opposite directionsfrom the outermost ends of said legs and connecting said cables throughthe length of said legs to winches on the platform, flooding theoutermost ends of said legs with water and controlling the lateralforces on the legs with said transverse cables to pivot said legs into anearly vertical position, until the outermost ends of said legs engagethe bottom of the ocean floor, and expelling water from said legs toincrease their buoyancy for lifting said platform out of said waterwhile pivoting said legs to an anchoring position and maintaining thecenter of buoyancy above the center of gravity for the assembly.
 10. Themethod as defined in claim 9 and further including the step of floatinga conductor bundle to the site location in a horizontal condition wheresaid bundle has buoyancy chambers for control flooding of water, at thesite location, after the platform is raised, flooding the outermost endof said conductor bundle while fixing the location of the other endrelative to the platform until the conductor bundle is in a verticalposition, maintaining said bundle in a vertical position off of theocean floor and moving said bundle into location relative to saidplatform module, and filling said bundle with water to set it inlocation for well operations.
 11. A method for erecting an offshoreplatform in deep water comprising the steps of floating separate modulesof said platform to an offshore site where said modules include asurface platform and leg modules, said leg modules including buoyancychambers for controlled flooding and expelling of water, said legmodules further including mat modules pivotally interconnected to theoutermost ends of said leg modules, said mat modules having buoyancychambers for controlled flooding, flooding said mat modules so as tomaintain said mat modules in general horizontal alignment with thelength of said leg modules, at the offshore site, anchoring saidplatform at a site position, connecting all of the leg modules pivotallyto said platform while said leg modules are in a nearly horizontalposition, extending transverse cables in opposite directions from theoutermost ends of said leg modules and connecting said cables throughthe length of said leg modules to winches on the platform, flooding theoutermost ends of said leg modules with water and controlling thelateral forces on the leg modules with said transverse cables to pivotsaid leg modules into a nearly vertical position and maintaining saidmat modules in general horizontal alignment with the leg modules whilesaid leg modules are pivoted so that said mat modules are brought intoengagement with the ocean floor, and following the expelling of waterfrom said leg modules, the step of flooding said mat modules with waterto pivot said mat modules into anchoring position with the ocean floor.12. The method as defined in claim 11 and further including the step ofinterconnecting one end of chains extending from each of said legs atthe platform where the chains extend along the length of a leg and passover a pulley at the outermost end of a leg and return to the oTher endof the leg, and after interconnecting the one end of said chains, takingup the slack in the other ends of said chains to position said chains asan interconnection between the outermost ends of said legs.
 13. A marineplatform for deep water installation comprising a surface platformmodule, at least four supporting leg modules disposed at locations lyingon perpendicular, intersecting, horizontal axes, means pivotallyconnecting one end of said leg modules to said surface platform module,said pivot means respectively having pivot axis at said locations in aposition normal to an axis, each of said leg modules including tubularmembers arranged in an equidistant triangular relationship withinterconnecting support members, each of said tubular members includingbuoyancy compartments, and means for selectively flooding said buoyancycompartments with sea water.